updating with drush, md5 checksum error

I got that error too. Please help. Thanks!

File conditional_fields-7.x-3.x-dev.tar.gz is corrupt (wrong md5     [error]
checksum)

Can you be more specific about the command used? I tried "drush dl conditional_fields" and "drush up conditional_fields", they both work fine (using drush 5.4).

I got this error just now:

[aaron@zaphod default]$ drush up conditional_fields
... snip ...

Code updates will be made to the following projects: Conditional Fields [conditional_fields-7.x-3.x-dev]

Note: A backup of your project will be stored to backups directory if it is not managed by a supported version control system.
Note: If you have made any modifications to any file that belongs to one of these projects, you will have to migrate those modifications after updating.
Do you really want to continue with the update process? (y/n): y
File conditional_fields-7.x-3.x-dev.tar.gz is corrupt (wrong md5     [error]
checksum).
Updating project conditional_fields failed. Attempting to roll back  [error]
to previously installed version.
Backups were restored successfully.                                  [ok]

[aaron@zaphod default]$ drush version
drush version 5.4

[aaron@zaphod default]$ drush version
drush version 5.4

Duplicate of #1630220: Cache inconsistency lead to "wrong md5 checksum" on dev releases